It is often desirable to precisely position an object, such as a slide of a microscope stage, in a manner which provides suitable movement thereof at a relatively high rate of speed to precise positions in an accurate and reliable manner. For example, in the application of image processing to the field of automatic cytology, it is desirable to locate and classify particular cell types by moving a slide containing such cells under a microscope at an average rate of about one cell per second with an accuracy equalling or surpassing that of a human technician. The operator should be able to view the cell which is being classified in order to verify performance as well as to make occasional decisions with respect thereto. Use of a mechanical positioning device in a cytological application, for example, may require the slide to be mechanically located to within 10 micrometers.
While conventional stepping motors have been suggested for use in moving the slide along one or more axes, such devices are insufficient to provide the desired high speed movement of the slide across its dimensions. For example, when using step motors which can move at their normal capabilities at rates of 200 microns per second, a 25 mm. slide requires approximately two minutes to move thereacross. Even when the capabilities of the step motor drives are increased essentially to their limits, the rate of movement increases only to the extent that a 25 mm. slide, for example, would still require at least 6 seconds to move across the field of the microscope.
However, the high speed requirements of some cytological applications, for example, require speeds which would permit travel across the 25 mm. slide in approximately one-half second, a requirement which does not appear to be within the capabilities of any known stepping motor devices.